1. Field of the Invention
This invention relates to cameras, and particularly, to a camera motor drive which performs film winding and shutter energizing operations.
2. Description of Prior Art
In one type of conventional automatic camera film winder, the winder is started upon completion of the shutter closing process and then stopped upon having completed the winding of a frame of film; the shutter is then released immediately after completion of the film winding process. However, immediately after completion of a film winding action, each part of the film winding mechanism still remains loaded or stressed, i.e., in motion, because of the inertia of the motor and the winding mechanism. Hence, if the shutter release starts immediately after a film winding action, the film is likely to be exposed to light before it actually stops. Such a conventional arrangement thus introduces the possibility of blurred pictures.
In addition to this problem, with the coupled parts of a shutter release mechanism and the film winding mechanism being in a stressed condition, each mechanism might be prevented from operating smoothly or might even be rendered inoperative. To eliminate these difficulties, it is desirable to remove the stressed or loaded condition. During non-continuous operation, one frame of film at a time is used, thus obviating the stressed condition because a sufficiently long period of time elapses between completion of film winding and shutter release. The condition is also absent after the last frame of film has been wound in a continuous photographic operation.
A conventional automatic film winding device is provided with a sliding clutch in its transmission gear mechanism and is arranged to absorb any excessive load or stress developed after completion of a film winding action because of the sliding action thereof removing the strain resulting from the film winding action. However, this method involves detecting the excessive stress after it has occurred. This response to detecting the completion of a film winding action results in delays. Besides, the provision of the sliding clutch in the film winding gear complicates the film winding mechanism and hinders efforts to reduce the size of the device. Furthermore, an excessive load is imposed on the motor by initiation of the sliding action of the sliding clutch and this overload on the motor makes adjustment thereof difficult. Also, the use of such a sliding clutch during a continuous picture taking sequence with an electromagnetic release type camera tends to expose the film to light during operation of the sliding clutch because shutter release begins immediately after a film winding action. In order to prevent this, the shutter release is arranged to begin in response to a signal representing completion of operation of the sliding clutch. A delay in the completion of a film winding action would occur after the film is actually wound and the film feed speed would then be decreased.
An attempt to solve these problems appears in Japanese Laid Open Patent Application, Publication No. 53-39123 which discloses an electric film winding device. In this device, an electromagnetic clutch, disposed in a film winding gear driving mechanism, is arranged to be turned off, upon completion of a film winding action, to disconnect the winding gear of the motor and prevent it from being overloaded. In this prior art device, the electromagnetic clutch is off when non-energized and is turned on when energized. The power supply to the clutch is cut off every time a winding action is completed. In carrying out a continuous photographic operation, the overloading which otherwise takes place every time a film winding action is completed, is effectively prevented by the electromagnetic clutch before the next exposure is initiated so that transition to the next exposure can be effected in a short period of time.
However, in a non-continuous picture taking operation, or before starting a continuous picture taking operation following a non-continuous operation, an ample length of time exists between a photographic operating cycle on one film frame and the next cycle on another, ie., before the next exposure action and the next film winding action. In such a case, the arrangement for operating an electromagnetic clutch to prevent overload is unnecessary. Even if an overloaded condition arises, upon completion of a film winding action, which is performed after completion of a non-continuous, single-frame, photographic operation, the overload can be eliminated during this amply long time interval before the next operation and the overloaded condition thus disappears in time. Hence, the electromagnetic clutch which turns off every time a film winding action is completed, wastes electric power as it operates even when its operation is not required. Moreover, in this example of the prior art, the electromagnetic clutch is disposed directly within the film winding gear driving mechanism. This arrangement necessitates having the electromagnetic clutch intermittently turning the transmission torque on and off, making the size of the clutch relatively large. The relatively large size of the electromagnetic clutch introduces the problem of placing it in the limited space of a compact electric motor drive film winder.